The present invention relates to compositions and methods for treating pain, including bone tumor pain. In particular, the present invention relates to Clostridial toxin derivatives, methods for making the Clostridial toxin derivatives, and methods for treating pain using the Clostridial toxin derivatives.
Many, if not most, aliments of the body cause pain. The causes of pain can include inflammation, muscle spasm and the onset of a neuropathic event or syndrome. Inflammatory pain can occur when tissue is damaged, as can result from surgery or due to an adverse physical, chemical, or thermal event or to infection by a biologic agent. Spasticity or muscle spasm can be a serious complication of trauma to the spinal cord or other disorders that create damage within the spinal cord. Muscle spasm is often accompanied by pain. The pain experienced during a muscle spasm can result from the direct effect of the muscle spasm stimulating mechanosensitive pain receptors or from the indirect effect of the spasm compressing blood vessels and causing ischemia. Since the spasm increases the rate of metabolism in the affected muscle tissue, the relative ischemia becomes greater creating thereby conditions for the release of pain inducing substances. Neuropathic pain is a persistent or chronic pain syndrome that can result from damage to the nervous system, the peripheral nerves, the dorsal root ganglion or dorsal root, or to the central nervous system.
Neuropathic pain syndromes include allodynia, various neuralgias such as post herpetic neuralgia and trigeminal neuralgia, phantom pain, and complex regional pain syndromes, such as reflex sympathetic dystrophy and causalgia. Causalgia is characterized by spontaneous burning pain combined with hyperalgesia and allodynia.
Pain can be experienced when the free nerve endings which constitute the pain receptors in the skin as well as in certain internal tissues are subjected to mechanical, thermal, or chemical stimuli. The pain receptors transmit signals along afferent neurons into the central nervous system and thence to the brain.
The transduction of sensory signals, such as pain signals, from the periphery to sensation itself is achieved by a multi-neuronal pathway and the information processing centers of the brain. The first nerve cells of the pathway involved in the transmission of sensory stimuli are called primary sensory afferents. The cell bodies for the primary sensory afferents from the head and some of the internal organs reside in various ganglia associated with the cranial nerves, particularly the trigeminal nuclei and the nucleus of the solitary tract. The cell bodies for the primary sensory afferents for the remainder of the body lie in the dorsal root ganglia of the spinal column. The primary sensory afferents and their processes have been classified histologically; the cell bodies fall into two classes: (1) A-types, and (2) B-types. The cell bodies of A-types are relatively large (60-120 micrometer in diameter) while the cell bodies of B-types are smaller (14-30 micrometer) and more numerous. Similarly the processes fall into two categories: (1) C-fibers, and (2) A-fibers. C-fibers lack the myelin sheath that A-fibers possess. A-fibers can be further sub-divided into A beta-fibers, that are large diameters with well developed myelin, and A delta-fibers, that are thinner with less well developed myelin. It is generally believed that A beta-fibers arise from A-type cell bodies and that A delta- and C-fibers arise from B-type cell bodies.
After the activation of the primary sensory afferents the next step in the transduction of sensory signals is the activation of the projection neurons, which carry the signal, via the spinothalamic tract, to higher parts of the central nervous system such as the thalamic nuclei. The cell bodies of these neurons (other than those related to the cranial nerves) are located in the dorsal horn of the spinal cord. This is also where the synapses between the primary afferents and the projection neurons are located. The dorsal horn is organized into a series of laminae that are stacked, with lamina I being most dorsal followed by lamina II, etc. The different classes of primary afferents make synapses in different laminae. For cutaneous primary afferents, C-fibers make synapses in laminae I and II, A delta-fibers in laminae I, II, and V, and A beta-fibers in laminae III, IV, and V. Deeper laminae (V-VII, X) are thought to be involved in the sensory pathways arriving from deeper tissues such as muscles and the viscera.
The predominant neurotransmitters at the synapses between primary afferents and projection neurons are substance P, glutamate, calcitonin-gene related peptide (CGRP), and neuropeptide Y. The efficiency of transmission of these synapses can be altered via descending pathways and by local intemeurons in the spinal cord. These modulatory neurons release a number of mediators that are either inhibitory (e.g. opioid peptides, glycine) or excitatory (e.g. nitric oxide, cholecystokinin), to provide a mechanism for enhancing or reducing awareness of sensations.
Effective pain alleviating drugs are needed. It is known that intraspinal administration of opioids, such as morphine and fentanyl can alleviate pain. See e.g. Gianno, J., et al., Intrathecal Drug Therapy for Spasticity and Pain, Springer-Verlag (1996) (which publication is incorporated herein by reference in its entirety). Unfortunately, current drugs used in intraspinal, or intrathecal, injections typically have only short lived antinociceptive effects. As a result, these drugs have to be frequently administered, such as by the aid of a pump for continuous infusion. For example, one frequently used pump is the SynchroMed(copyright) Infusion System, a programmable, implanted pump available from Medtronic, Inc., of Minneapolis, Minn. However, complications can arise due to the required surgical implantation procedure for the use of the pump and the known intrathecally administered drugs for pain, such as opioids, have the disadvantages of dependency and potential respiratory depression.
Longer acting analgesics are also known, for example, blocks by phenol injection. However, such treatments raise a considerable risk of irreversible functional impairment.
Intrathecal administration of botulinum toxin type B to mice to treat thermal hyperalgesia is known. Br. J. Pharmacol 1999;127(2):449-456. Additionally, it has been reported (Science, 1999; 286:1558-1561) (xe2x80x9cNichols et al.xe2x80x9d) that intrathecal injection of a cytotoxic saporin-substance P (saporin can be abbreviated as xe2x80x9cSAPxe2x80x9d and substance P can be abbreviated as xe2x80x9cSPxe2x80x9d) conjugate (which can be abbreviated as SAP-SP) results in a reduction of thermal hyperalgesia and mechanical allodynia.
As discussed Nichols et al, supra, spinothalamic and spinoparabrachial neurons are involved in the ascending conduction of acute noxious stimuli. Apparently, these neurons are projection neurons can be targeted by substance P. When a conjugate of the ribosome-inactivating protein saporin and SP was intrathecally infused into the spinal cord, the SAP-SP conjugate is stated to have specifically concentrated in the projection neurons, apparently because these neurons express cell surface receptors for substance P (a substance P receptor can be abbreviated as xe2x80x9cSPRxe2x80x9d). Unfortunately, the SAP-SP targeted neurons are killed by the SAP.
Although SAP-SP is specific for projection neurons because projection neurons appear to express the SPR, an intrathecal injection of SAP-SP may cause necrosis of other neurons through non-specific or low affinity SAP-SP neuronal interactions. For example, SAP-SP may interact with and cause motor neurons cell death. Since motor neurons and most other neurons in the spinal cord do not regenerate, it is contraindicated to use SAP-SP in humans, unless destruction of the neurons with the resulting in permanent disablement, and for example, paralysis, is a desired end result. Clearly it would be desirable to be able to treat pain, including chronic pain, without causing necrosis and irreversible loss of the neurons treated.
Botulinum Toxin
The anaerobic, gram positive bacterium Clostridium botulinum produces a potent polypeptide neurotoxin, botulinum toxin, which causes a neuroparalytic illness in humans and animals referred to as botulism. The spores of Clostridium botulinum are found in soil and can grow in improperly sterilized and sealed food containers of home based canneries, which are the cause of many of the cases of botulism. The effects of botulism typically appear 18 to 36 hours after eating the foodstuffs infected with a Clostridium botulinum culture or spores. The botulinum toxin can apparently pass unattenuated through the lining of the gut and attack peripheral motor neurons. Symptoms of botulinum toxin intoxication can progress from difficulty walking, swallowing, and speaking to paralysis of the respiratory muscles and death.
Botulinum toxin type A is the most lethal natural biological agent known to man. About 50 picograms of botulinum toxin (purified neurotoxin complex) type A is a LD50 in mice. One unit (U) of botulinum toxin is defined as the LD50 upon intraperitoneal injection into female Swiss Webster mice weighing 18-20 grams each. In other words, one unit of botulinum toxin is the amount of botulinum toxin that kills 50% of the group of female Swiss Webster mice. Seven immunologically distinct botulinum neurotoxins have been characterized, these being respectively botulinum neurotoxin serotypes A, B, C1, D, E, F and G each of which is distinguished by neutralization with type-specific antibodies. The different serotypes of botulinum toxin vary in the animal species that they affect and in the severity and duration of the paralysis they evoke. For example, it has been determined that botulinum toxin type A is 500 times more potent, as measured by the rate of paralysis produced in the rat, than is botulinum toxin type B. Additionally, botulinum toxin type B has been determined to be non-toxic in primates at a dose of 480 U/kg which is about 12 times the primate LD50 for botulinum toxin type A. Botulinum toxin apparently binds with high affinity to cholinergic motor neurons, is translocated into the neuron and blocks the release of acetylcholine.
Botulinum toxins have been used in clinical settings for the treatment of neuromuscular disorders characterized by hyperactive skeletal muscles. Botulinum toxin type A has been approved by the U.S. Food and Drug Administration for the treatment of blepharospasm, strabismus, and hemifacial spasm. Non-type A botulinum toxin serotypes apparently have a lower potency and/or a shorter duration of activity as compared to botulinum toxin type A. Clinical effects of peripheral intramuscular botulinum toxin type A are usually seen within one week of injection. The typical duration of symptomatic relief from a single intramuscular injection of botulinum toxin type A averages about three months.
Although all the botulinum toxins serotypes apparently inhibit release of the neurotransmitter acetylcholine at the neuromuscular junction, they do so by affecting different neurosecretory proteins and/or cleaving these proteins at different sites. For example, botulinum types A and E both cleave the 25 kiloDalton (kD) synaptosomal associated protein (SNAP-25), but they target different amino acid sequences within this protein. Botulinum toxin types B, D, F and G act on vesicle-associated protein (VAMP, also called synaptobrevin), with each serotype cleaving the protein at a different site. Finally, botulinum toxin type C1 has been shown to cleave both syntaxin and SNAP-25. These differences in mechanism of action may affect the relative potency and/or duration of action of the various botulinum toxin serotypes.
Regardless of serotype, the molecular mechanism of toxin intoxication appears to be similar and to involve at least three steps or stages. In the first step of the process, the toxin binds to the presynaptic membrane of the target neuron through a specific interaction between the H chain and a cell surface receptor; the receptor is thought to be different for each type of botulinum toxin and for tetanus toxin. The carboxyl end segment of the H chain, Hc, appears to be important for targeting of the toxin to the cell surface.
In the second step, the toxin crosses the plasma membrane of the poisoned cell. The toxin is first engulfed by the cell through receptor-mediated endocytosis, and an endosome containing the toxin is formed. The toxin then escapes the endosome into the cytoplasm of the cell. This last step is thought to be mediated by the amino end segment of the H chain, HN, which triggers a conformational change of the toxin in response to a pH of about 5.5 or lower. Endosomes are known to possess a proton pump which decreases intra endosomal pH. The conformational shift exposes hydrophobic residues in the toxin, which permits the toxin to embed itself in the endosomal membrane. The toxin then translocates through the endosomal membrane into the cytosol.
The last step of the mechanism of botulinum toxin activity appears to involve reduction of the disulfide bond joining the H and L chain. The entire toxic activity of botulinum and tetanus toxins is contained in the L chain of the holotoxin; the L chain is a zinc (Zn++) endopeptidase which selectively cleaves proteins essential for recognition and docking of neurotransmitter-containing vesicles with the cytoplasmic surface of the plasma membrane, and fusion of the vesicles with the plasma membrane. Tetanus neurotoxin, botulinum toxin/B/D,/F, and/G cause degradation of synaptobrevin (also called vesicle-associated membrane protein (VAMP)), a synaptosomal membrane protein. Most of the VAMP present at the cytosolic surface of the synaptic vesicle is removed as a result of any one of these cleavage events. Each toxin specifically cleaves a different bond.
The molecular weight of the botulinum toxin protein molecule, for all seven of the known botulinum toxin serotypes, is about 150 kD. Interestingly, the botulinum toxins are released by Clostridial bacterium as complexes comprising the 150 kD botulinum toxin protein molecule along with associated non-toxin proteins. Thus, the botulinum toxin type A complex can be produced by Clostridial bacterium as 900 kD, 500 kD and 300 kD forms. Botulinum toxin types B and C1 is apparently produced as only a 500 kD complex. Botulinum toxin type D is produced as both 300 kD and 500 kD complexes. Finally, botulinum toxin types E and F are produced as only approximately 300 kD complexes. The complexes (i.e. molecular weight greater than about 150 kD) are believed to contain a non-toxin hemaglutinin protein and a non-toxin and non-toxic nonhemaglutinin protein. These two non-toxin proteins (which along with the botulinum toxin molecule comprise the relevant neurotoxin complex) may act to provide stability against denaturation to the botulinum toxin molecule and protection against digestive acids when toxin is ingested. Additionally, it is possible that the larger (greater than about 150 kD molecular weight) botulinum toxin complexes may result in a slower rate of diffusion of the botulinum toxin away from a site of intramuscular injection of a botulinum toxin complex.
In vitro studies have indicated that botulinum toxin inhibits potassium cation induced release of both acetylcholine and norepinephrine from primary cell cultures of brainstem tissue. Additionally, it has been reported that botulinum toxin inhibits the evoked release of both glycine and glutamate in primary cultures of spinal cord neurons and that in brain synaptosome preparations botulinum toxin inhibits the release of each of the neurotransmitters acetylcholine, dopamine, norepinephrine, CGRP and glutamate.
Botulinum toxin type A can be obtained by establishing and growing cultures of Clostridium botulinum in a fermenter and then harvesting and purifying the fermented mixture in accordance with known procedures. All the botulinum toxin serotypes are initially synthesized as inactive single chain proteins which must be cleaved or nicked by proteases to become neuroactive. The bacterial strains that make botulinum toxin serotypes A and G possess endogenous proteases and serotypes A and G can therefore be recovered from bacterial cultures in predominantly their active form. In contrast, botulinum toxin serotypes C1, D and E are synthesized by nonproteolytic strains and are therefore typically unactivated when recovered from culture. Serotypes B and F are produced by both proteolytic and nonproteolytic strains and therefore can be recovered in either the active or inactive form. However, even the proteolytic strains that produce, for example, the botulinum toxin type B serotype only cleave a portion of the toxin produced. The exact proportion of nicked to unnicked molecules depends on the length of incubation and the temperature of the culture. Therefore, a certain percentage of any preparation of, for example, the botulinum toxin type B toxin is likely to be inactive, possibly accounting for the known significantly lower potency of botulinum toxin type B as compared to botulinum toxin type A. The presence of inactive botulinum toxin molecules in a clinical preparation will contribute to the overall protein load of the preparation, which has been linked to increased antigenicity, without contributing to its clinical efficacy. Additionally, it is known that botulinum toxin type B has, upon intramuscular injection, a shorter duration of activity and is also less potent than botulinum toxin type A at the same dose level.
It has been reported that botulinum toxin type A has been used in clinical settings as follows:
(1) about 75-125 units of BOTOX(copyright)1 per intramuscular injection (multiple muscles) to treat cervical dystonia;
(2) 5-10 units of BOTOX(copyright) per intramuscular injection to treat glabellar lines (brow furrows) (5 units injected intramuscularly into the procerus muscle and 10 units injected intramuscularly into each corrugator supercilii muscle);
(3) about 30-80 units of BOTOX(copyright) to treat constipation by intrasphincter injection of the puborectalis muscle;
(4) about 1-5 units per muscle of intramuscularly injected BOTOX(copyright) to treat blepharospasm by injecting the lateral pre-tarsal orbicularis oculi muscle of the upper lid and the lateral pre-tarsal orbicularis oculi of the lower lid.
(5) to treat strabismus, extraocular muscles have been injected intramuscularly with between about 1-5 units of BOTOX(copyright), the amount injected varying based upon both the size of the muscle to be injected and the extent of muscle paralysis desired (i.e. amount of diopter correction desired).
(6) to treat upper limb spasticity following stroke by intramuscular injections of BOTOX(copyright) into five different upper limb flexor muscles, as follows:
(a) flexor digitorum profundus: 7.5 U to 30 U
(b) flexor digitorum sublimus: 7.5 U to 30 U
(c) flexor carpi ulnaris: 10 U to 40 U
(d) flexor carpi radialis: 15 U to 60 U
(e) biceps brachii: 50 U to 200 U.
Each of the five indicated muscles has been injected at the same treatment session, so that the patient receives from 90 U to 360 U of upper limb flexor muscle BOTOX(copyright) by intramuscular injection at each treatment session.
1 Available from Allergan, Inc., of Irvine, Calif. under the tradename BOTOX(copyright). 
The success of botulinum toxin type A to treat a variety of clinical conditions has led to interest in other botulinum toxin serotypes. A study of two commercially available botulinum type A preparations (BOTOX(copyright) and Dysport(copyright)) and preparations of botulinum toxins type B and F (both obtained from Wako Chemicals, Japan) has been carried out to determine local muscle weakening efficacy, safety and antigenic potential. Botulinum toxin preparations were injected into the head of the right gastrocnemius muscle (0.5 to 200.0 units/kg) and muscle weakness was assessed using the mouse digit abduction scoring assay (DAS). ED50 values were calculated from dose response curves. Additional mice were given intramuscular injections to determine LD50 doses. The therapeutic index was calculated as LD50/ED50. Separate groups of mice received hind limb injections of BOTOX(copyright) (5.0 to 10.0 units/kg) or botulinum toxin type B (50.0 to 400.0 units/kg), and were tested for muscle weakness and increased water consumption, the later being a putative model for dry mouth. Antigenic potential was assessed by monthly intramuscular injections in rabbits (1.5 or 6.5 ng/kg for botulinum toxin type B or 0.15 ng/kg for BOTOX(copyright)). Peak muscle weakness and duration were dose related for all serotypes. DAS ED50 values (units/kg) were as follows: BOTOX(copyright): 6.7, Dysport(copyright): 24.7, botulinum toxin type B: 27.0 to 244.0, botulinum toxin type F: 4.3. BOTOX(copyright) had a longer duration of action than botulinum toxin type B or botulinum toxin type F. Therapeutic index values were as follows: BOTOX(copyright): 10.5, Dysport(copyright): 6.3, botulinum toxin type B: 3.2. Water consumption was greater in mice injected with botulinum toxin type B than with BOTOX(copyright), although botulinum toxin type B was less effective at weakening muscles. After four months of injections, 2 of 4 (where treated with 1.5 ng/kg) and 4 of 4 (where treated with 6.5 ng/kg) rabbits developed antibodies against botulinum toxin type B. In a separate study, 0 of 9 BOTOX(copyright) treated rabbits demonstrated antibodies against botulinum toxin type A. DAS results indicate relative peak potencies of botulinum toxin type A being equal to botulinum toxin type F, and botulinum toxin type F being greater than botulinum toxin type B. With regard to duration of effect, botulinum toxin type A was greater than botulinum toxin type B, and botulinum toxin type B duration of effect was greater than botulinum toxin type F. As shown by the therapeutic index values, the two commercial preparations of botulinum toxin type A (BOTOX(copyright) and Dysport(copyright)) are different. The increased water consumption behavior observed following hind limb injection of botulinum toxin type B indicates that clinically significant amounts of this serotype entered the murine systemic circulation. The results also indicate that in order to achieve efficacy comparable to botulinum toxin type A, it is necessary to increase doses of the other serotypes examined. Increased dosage can comprise safety. Furthermore, in rabbits, type B was more antigenic than was BOTOX(copyright), possibly because of the higher protein load injected to achieve an effective dose of botulinum toxin type B.
The tetanus neurotoxin acts mainly in the central nervous system, while botulinum neurotoxin acts at the neuromuscular junction; both act by inhibiting acetylcholine release from the axon of the affected neuron into the synapse, resulting in paralysis. The effect of intoxication on the affected neuron is long-lasting and until recently has been thought to be irreversible. The tetanus neurotoxin is known to exist in one immunologically distinct type.
Acetylcholine
Typically only a single type of small molecule neurotransmitter is released by each type of neuron in the mammalian nervous system. The neurotransmitter acetylcholine is secreted by neurons in many areas of the brain, but specifically by the large pyramidal cells of the motor cortex, by several different neurons in the basal ganglia, by the motor neurons that innervate the skeletal muscles, by the preganglionic neurons of the autonomic nervous system (both sympathetic and parasympathetic), by the postganglionic neurons of the parasympathetic nervous system, and by some of the postganglionic neurons of the sympathetic nervous system. Essentially, only the postganglionic sympathetic nerve fibers to the sweat glands, the piloerector muscles and a few blood vessels are cholinergic and most of the postganglionic neurons of the sympathetic nervous system secret the neurotransmitter norepinephine. In most instances acetylcholine has an excitatory effect. However, acetylcholine is known to have inhibitory effects at some of the peripheral parasympathetic nerve endings, such as inhibition of the heart by the vagal nerve.
The efferent signals of the autonomic nervous system are transmitted to the body through either the sympathetic nervous system or the parasympathetic nervous system. The preganglionic neurons of the sympathetic nervous system extend from preganglionic sympathetic neuron cell bodies located in the intermediolateral horn of the spinal cord. The preganglionic sympathetic nerve fibers, extending from the cell body, synapse with postganglionic neurons located in either a paravertebral sympathetic ganglion or in a prevertebral ganglion. Since, the preganglionic neurons of both the sympathetic and parasympathetic nervous system are cholinergic, application of acetylcholine to the ganglia will excite both sympathetic and parasympathetic postganglionic neurons.
Acetylcholine activates two types of receptors, muscarinic and nicotinic receptors. The muscarinic receptors are found in all effector cells stimulated by the postganglionic neurons of the parasympathetic nervous system, as well as in those stimulated by the postganglionic cholinergic neurons of the sympathetic nervous system. The nicotinic receptors are found in the synapses between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic. The nicotinic receptors are also present in many membranes of skeletal muscle fibers at the neuromuscular junction.
Acetylcholine is released from cholinergic neurons when small, clear, intracellular vesicles fuse with the presynaptic neuronal cell membrane. A wide variety of non-neuronal secretory cells, such as, adrenal medulla (as well as the PC12 cell line) and pancreatic islet cells release catecholamines and insulin, respectively, from large dense-core vesicles. The PC12 cell line is a clone of rat pheochromocytoma cells extensively used as a tissue culture model for studies of sympathoadrenal development. Botulinum toxin inhibits the release of both types of compounds from both types of cells in vitro, permeabilized (as by electroporation) or by direct injection of the toxin into the denervated cell. Botulinum toxin is also known to block release of the neurotransmitter glutamate from cortical synaptosomes cell cultures.
U.S. Pat. No. 5,989,545 (xe2x80x9cFoster et al.xe2x80x9d) (incorporated herein by reference in its entirety) discusses conjugating clostridial neurotoxins to targeting moieties in order to direct the inhibitory effect of clostridial neurotoxins toward primary sensory afferent neurons. Thus, the mechanism by which the agents disclosed by Foster et al alleviate pain is as follows: the targeting moieties of the agents, for example the growth factors, bind to receptor sites on the sensory afferent nerve terminals, for example the growth factor receptors, in the spinal cord; then, the clostridial neurotoxins, along with the conjugated targeting moieties, translocate into the nerve terminal and inhibit the release of one or more transmitters involved in the signaling of pain, and thereby alleviate pain.
Unlike SAP-SP, the clostridial-targeting moiety conjugates disclosed by Foster et al do not appear to be cytotoxic. Despite their superiority to the SAP-SP in that they are non-cytotoxic, they are still inadequate as pain alleviating agents because they lack the specificity for treating pain. More particularly, the Foster et al""s targeting moieties intended for primary sensory afferent neurons are non-specific.
Thus, the agents disclosed by Foster et al are non-specific because their targeting moieties are not known to bind to receptors specifically and to primarily localize to primary sensory afferent nerve terminals. Therefore, the targeting moieties disclosed by Foster et al. may readily bind to receptors on neuronal terminals, or neurons, that are not primary sensory afferent synaptic terminals. For example, the targeting moiety comprising nerve growth factor disclosed by Foster may readily bind to receptors on nerve terminals and neurons other than the receptors on the primary sensory afferent nerve terminals, because nerve growth factor receptors are found on most neurons. As such, the clostridial neurotoxin conjugate disclosed by Foster et al may bind to one of these other neurons, for example the neurons involved in the sympathetic pathway, translocate into their cytosol, inhibit the release of their neurotransmitters, and thereby inhibiting their functions. Such random, non-specific inhibition may cause undesirable side effects during the treatment of pain.
Similarly, bradykinin, another targeting moieties disclosed by Foster et al, have been shown to have high density concentration in the motor neurons of the ventral horn in the spinal cord. (See Lopes et al, Neuroscience 78(2):481-497, the content of which is incorporated in its entirety herein by reference.) Agents disclosed by Foster et al which bear bradykinins as targeting moieties will significantly interact and interfere with motor functions when the agents are injected intraspinally to treat pain.
Also, the opioid receptor binding targeting moieties disclosed by Foster et al, for example, methionine-enkephalin, are non-specific with respect to directing the clostridial neurotoxin to the primary sensory afferent nerve terminal. Kandel et al, Principles of Neural Science, third edition, page 395, (1991), indicated that opioid receptors are widely distributed throughout the central nervous system, suggesting that opioid receptors, when activated, modulate physiological functions other than pain. Therefore, the clostridial neurotoxin-targeting moiety, as disclosed by Foster el al, may bind to and interfere with cells having opioid receptors but are not involved in the pain pathway. When this non-specific binding and interference occur, undesirous side effects may result.
What is needed therefore is an specific (high affinity) therapeutically effective, long duration non-cytotoxic agent and method for treating pain.
The present invention meets this need by providing specific (high affinity) therapeutically effective, long duration non-cytotoxic agents and methods for treating pain. I have discovered agents effective in alleviating pain, methods of making such agents and methods of using such agents to alleviate pain. The present invention provides non-cytotoxic agents for treating pain which preferably have one or more of the characteristics of long duration of activity and specificity for the treatment of pain with limited or substantially insignificant side effects at therapeutic dose levels. Furthermore, the methods of producing these agents are relatively straight forward and effective to provide the desired results.
In one embodiment of the invention, methods for treating pain in a subject, comprise administering an agent to the subject, wherein the agent comprises a botulinum toxin component covalently coupled to substance P. In a further embodiment, the botulinum toxin component comprises the proteolytic domain of the botulinum toxin. In another embodiment, the botulinum toxin component comprises the proteolytic domain and translocational domain of the botulinum toxin. In yet a further embodiment, the proteolytic domain is covalently coupled to the translocational domain.
In another embodiment, the invention provides methods for reducing pain in a subject, comprising administering an agent to a subject, wherein the agent comprises a botulinum toxin component coupled to substance P. In yet another embodiment, the agent comprises a botulinum toxin proteolytic domain covalently attached to a botulinum toxin translocational domain, and substance P covalently attached to the translocational domain.
In practicing the foregoing methods, the botulinum toxin component is preferably selected from a group of botulinum toxin serotypes consisting of serotype A, serotype B, serotype C1, serotype D, serotype E, serotype F, and serotype G. In a preferred embodiment, the botulinum toxin component is botulinum toxin serotype A. In one embodiment of the invention, the botulinum toxin component comprises an HN and an L chain of the botulinum toxin. The HN chain is preferably obtained from a botulinum toxin selected from the group consisting of botulinum toxin serotype A, serotype B, serotype C1, serotype D, serotype E, serotype F, and serotype G.
In yet another embodiment of the invention, methods for reducing pain in a subject, comprise administering an agent to the subject, wherein the agent comprises a botulinum toxin type A proteolytic domain covalently attached to a botulinum toxin type A translocational domain, and substance P covalently attached to the translocational domain.
In additional embodiments of the invention, the botulinum toxin component may be coupled to a precursor or analogues of substance P.
In a preferred embodiment of the invention, the proteolytic domain is a botulinum toxin type A proteolytic domain. In yet another embodiment of the invention, the translocational domain is a botulinum toxin type A translocational domain. In a further embodiment of the invention, the proteolytic and translocational domains are botulinum toxin type A proteolytic and translocational domains. In practicing the foregoing methods, the agent may be administered before, or after, the onset of a nociceptive event experienced by the subject. An example of a nociceptive event includes a neuropathic pain syndrome, such as inflammatory pain.
In practicing the foregoing methods, the agent of the invention can be administered intramusclarly and/or intrathecally. The amount of agent administered may reduce the pain in a subject by about 20%. In a preferred embodiment, the agent reduces the pain in the patient by about 50%. In a more preferred embodiment, the agent reduces the pain in the patient by about 80%.
In another broad aspect of this invention, there are provided methods for treatment of a bone tumor. A preferable treatment of bone tumor includes the treatment of, for example, pain associated with the bone tumor, which comprise administering effective doses of the agents according to the invention. The routes of administration preferably include administration locally to the peripheral location of pain, particularly to a bone tumor or the vicinity of a bone tumor.
Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.
Definitions
Light chain means the light chain of a clostridial neurotoxin. It has a molecular weight of about 50 kDa, and can be referred to as L chain, L, or as the proteolytic domain (amino acid sequence) of a clostridial neurotoxin.
Heavy chain means the heavy chain of a clostridial neurotoxin. It has a molecular weight of about 100 kDa and can be referred to as H chain, or as H.
Hc means a fragment (about 50 kDa) derived from the H chain of a clostridial neurotoxin which is approximately equivalent to the carboxyl end segment of the H chain, or the portion corresponding to that fragment in the intact H chain. It is believed to be immunogenic and to contain the portion of the natural or wild type clostridial neurotoxin involved in high affinity, presynaptic binding to motor neurons.
HN means a fragment (about 50 kDa) derived from the H chain of a clostridial neurotoxin which is approximately equivalent to the amino end segment of the H chain, or the portion corresponding to that fragment in the intact in the H chain. It is believed to contain the portion of the natural or wild type clostridial neurotoxin involved in the translocation of the L chain across an intracellular endosomal membrane.
LHN or L-HN means a fragment derived from a clostridial neurotoxin that contains the L chain, or a functional fragment thereof, coupled to the HN domain. It can be obtained from the intact clostridial neurotoxin by proteolysis, so as to remove or to modify the HC domain.
Targeting moiety means a molecule that has a specific binding affinity for a cell surface receptor, for example, for a neuronal receptor so as to influence the transmission or reception of pain signals by the neuron.
xe2x80x9cAboutxe2x80x9d means approximately or nearly and in the context of a numerical value set forth herein means xc2x110% of the numerical value or range recited or claimed.
xe2x80x9cBone tumorxe2x80x9d means a neoplasm located on or within a bone.
xe2x80x9cLocal administrationxe2x80x9d means direct administration by a non-systemic route at or in the vicinity of the site of an affliction, disorder, or perceived pain.
As used herein, an xe2x80x9cagentxe2x80x9d is defined as a modified neurotoxin that possesses biological activity that is similar, or substantially similar, to a biological activity of the unmodified neurotoxin. The modified neurotoxin is said to be xe2x80x9csubstantially similarxe2x80x9d to another neurotoxin if both neurotoxins have similar structures, or if both neurotoxins possess a similar biological activity. For example, a biological activity of a neurotoxin includes the binding of the neurotoxin to a receptor on a neural cell, and interfering with the normal function of the neural cell. Examples of normal functions of neurons include action potential discharge, and neurotransmission, including synaptic transmission. A neurotoxin can inhibit action potential discharge. A neurotoxin may also inhibit synaptic neurotransmission. One example of a neurotoxin is a botulinum toxin. A modified neurotoxin is a neurotoxin that has been changed from its natural state. Modified neurotoxins include analogs and fragments of neurotoxins. Modified neurotoxins can be naturally-made or recombinantly-made. One example of a modified neurotoxin, as disclosed herein, is botulinum toxin coupled to a substance P molecule.
Importantly, the agents disclosed herein are preferably administered by local administration, that is directly to the site where a therapeutic effect is desired.
This invention is based upon the discovery that pain, including bone tumor pain, can be treated by administration to a patient of an agent which is comprised of a derivative of a clostridial neurotoxin and a targeting moiety, where the targeting moiety is selected from the group consisting of transmission compounds which can be released from a neuron upon the initiation, transmission of, or facilitation of the generation of, a pain signal by the neuron.
Significantly, the agents of the present invention can alleviate pain without being cytotoxic to their target neurons. Furthermore, agents within the scope of the present invention can be administered to both central nociceptive neurons and to primary sensory afferent neurons
The mechanism of action for these agents in alleviating pain is currently not fully understood. Without wishing to limit the invention to any particular theory or mechanism of operation, it is believed that, at least with respect to areas in spinal cord, the agents disclosed herein target neurons having receptors for neurotransmitters that are released by neurons for or upon the transmission of pain signals. For example, when the targeting moiety is substance P, the agent is thought to interact with neurons expressing substance P receptors (SPR), such as projection neurons. Moreover, the receptors binding neurotransmitters released for the transmission of pain are primarily expressed on cells involved in the transmission of pain signals. For example, with respect to the central nervous system, it is well known that substance P receptors are primarily expressed on projection neurons in the dorsal horn of the spinal cord. See e.g. Vigna et al, J. Neuroscience, 14(2):834-845 (1994).
Therefore, the agents as described in this invention preferably are very specific for treating pain because they do not substantially or significantly interact and/or interfere with neurons and cells of other systems. Moreover, it is believed that the agents of this invention may enter into these specific neurons, for example projection neurons, through an endocytosis process. Once inside the neurons, it is further believed that the HN of these agents facilitate the translocation of the agent into the cytosol. In the cytosol, the agent, or a component thereof, can inhibit the release of a neurotransmitter involved in the further transmission of pain signals. It is further believed that the L chain of the clostridial neurotoxin component of the agent is responsible for the inhibition of the release of neurotransmitters that are involved in pain transmission by interfering with their vesicular exocytosis.
Additionally, the agents of this invention also provide pain alleviating effects when locally applied to peripheral pain sites. Also without wishing to limit the invention to any particular theory or mechanism of operation, it is believed that the agents interfere with the functions of cells having receptors for nociception, for example orphanin, substance P and/or kyotorphin, at the peripheral locations. See Ueda, Jpn J. Pharmacology, 79(3):263-268, the content of which is incorporated in its entirety herein by reference. These cells are uniquely involved in pain transmissions and the disruption of their functions by the agents can result in pain alleviation. Furthermore, it is believed that the mechanism for the inhibitory effects by agents in these cells is similar to that described above. Moreover, these agents can also bind, enter into and interfere with the function of primary sensory neurons.
According to one broad aspect of the invention, the clostridial neurotoxin component is covalently coupled to a targeting moiety. The clostridial neurotoxin component is a polypeptide and may be derived from Clostridial beratti, Clostridial butyricum, or Clostridial botulinum. More preferably, the clostridium neurotoxin component is derived from Clostridial botulinum. Clostridial botulinum produces botulinum toxin types A, B, C, D, E, F and G. Although any of these toxin types may be used in the present invention, botulinum type A is more preferably used.
Furthermore, the clostridial neurotoxin component may comprise only a fragment of the entire neurotoxin. For example, it is known in the art that the Hc of the neurotoxin molecule can be removed from the other segment of the H chain, the HN, such that the HN fragment remains disulphide linked to the L chain of the neurotoxin molecule to provide a fragment known as the LHN. Thus, in one embodiment of the present invention the LHN fragment of a clostridial neurotoxin is covalently coupled, using linkages which may include one or more spacer regions, to a targeting moiety.
In another embodiment of the invention, the domain having the Hc of a clostridial neurotoxin is removed, mutated or modified, e.g. by chemical modification, to reduce, or preferably incapacitate, its ability to bind the neurotoxin to receptors at the neuromuscular junction. This modified clostridial neurotoxin is then covalently coupled, using linkages which may include one or more spacer regions, to a targeting moiety.
In another embodiment of the invention, the H chain of a clostridial neurotoxin, in which the Hc is removed, mutated or modified, e.g. by chemical modification, to reduce, preferably incapacitate, its ability to bind the neurotoxin to receptors at the neuromuscular junction is combined with the L-chain of a different clostridial neurotoxin, to form a hybrid. For example, in one embodiment, the clostridial neurotoxin component comprises an H chain with the Hc removed, mutated or modified derived from botulinum toxin type A, and an L chain derived from another botulinum toxin type. The described hybrid is covalently coupled to a targeting moiety, preferably with one or more spacer regions.
In another embodiment of the invention the L chain of a clostridial neurotoxin, or a fragment of the L chain containing the endopeptidase activity, is linked, using linkages which may include one or more spacer regions, to a targeting moiety which can also effect the internalization of the L chain, or fragment thereof containing endopeptidase activity, into the cytoplasm of the cell.
In a preferred embodiment, the agent comprises the HN the L chain and the targeting moiety, covalently linked together. The targeting moiety according to the first aspect of the invention is preferably derived from amino acids, substituted counterparts thereof and mixtures thereof. The term xe2x80x9csubstituted counterparts thereofxe2x80x9d as it relates to any of the above noted amino acids refers to molecules that are functionally and physically similar to the amino acids, either as independent units or units incorporated into macromolecules, for example, peptides.
In one preferred aspect of the present invention, the targeting moiety is glutamate, since glutamate is the predominant neurotransmitter at the synapses between primary afferents and projection neurons. In another embodiment, the targeting moieties may be components that are substantially similar to the transmission compounds, for example, glutamate, in this particular instance. Hereinafter, the term xe2x80x9ccomponents that are substantially similar to the transmission compounds,xe2x80x9d is defined as molecules or substances that have the same functions as that of the transmission compounds, for example, binding to receptors that are involved in the transmission of pain signals.
In one embodiment, components that are substantially similar to glutamate are agonists of glutamate. For example, components substantially similar to glutamate are quisqualate, DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate, N-Me-D-aspartate, kinate and the like. Additionally, components substantially similar to glutamate may also include antagonists of glutamate. For example, these molecules include 6-cyano-7nitroquinozaline-2,3-dione, 3-(2-carboxypiperazin-4-yl)propyl-1-phosponic acid, lactonized kainate and the like.
In a more preferred embodiment, the amino acids link to form one of the peptides which are released by neurons for the transmission of pain signals. For example, these peptides include neuropeptide Y and calcitonin-gene related peptide (CGRP). Even more preferably, the peptide is substance P.
In another embodiment, components substantially similar to substance P may be used as targeting moieties. These components include substance P precursors, fragments, analogs and/or derivatives. The history, isolation, identification, and synthesis of substance P and its precursors, fragments, analogs and/or derivatives are disclosed in U.S. Pat. No. 5,891,842 (incorporated herein by reference in its entirety).
Substance P is an 11 amino acid peptide which has a number of different natural and synthetic precursor forms; has been demonstrated to be converted into a variety of naturally occurring amino-terminal peptide fragments; and can be obtained in analog format compromising, substituted counterparts thereof, for example, lysine methyl ester, D-amino acids or disulfide bridges substitutions, thereby yielding more stable and discriminating formulations. A representative listing of substance P and its related chemical entities is provided by Table I below. The amino acid sequence (1) in Table I (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-amide) can be referred to a SEQ ID NO:1, and the subsequent 17 amino acid sequences set forth in Table one can be similarly identified as SEQ ID NO:2 to SEQ ID NO:18.
The components substantially similar to substance P may also include molecules in the same family as that of substance P. For example, a preferred family of such molecules would be the tachykinin family to which substance P is a member. Examples of some family members of tachykinins include physalaemin, kassinin, uperolein, eledoisin, substance K and the like.
In a preferred embodiment, the agent comprises a clostridial neurotoxin component, for example LHN, coupled to substance P. In another preferred embodiment, the agent comprises a hybrid of two clostridial neurotoxins, such as the H chain, preferably HN, derived from botulinum toxin A and the L chain derived from another botulinum toxin, coupled to substance P. In another preferred embodiment, the clostridial component of the agent is a botulinum toxin type A in which the Hc has been removed or modified, coupled to substance P.
In another preferred embodiment, the agent comprises an L chain of a clostridial neurotoxin, or a fragment of the L chain containing the endopeptidase activity, coupled substance P. Even more preferably, the L chain or fragment of the L chain is derived from botulinum toxin A, and is coupled to substance P. Additionally, it is preferred that the L chain coupled to the substance P is covalently linked to HN.
The clostridial components and the targeting moieties are coupled by covalent linkages. In a preferred embodiment, the linkages may include appropriate spacer regions. Spacer regions have many functions within this invention. For example, one of the functions of the spacer regions is to provide for adequate distance between the clostridial neurotoxin components and the targeting moieties so that the two components can independently and freely move about, without an internal steric hindrance.
In one embodiment, the spacer region is made up of sugar molecules, for example, saccharides, glucose, etc. In another embodiment, the spacer region may be constructed from an aliphatic chain. In another embodiment, the spacer regions may be constructed by linking together a series of amino acids, preferably glycine because they are small and are devoid of any functional group. In yet another embodiment, the spacer region may comprise one or more of the sugar molecules, aliphatic chains, and amino acids.
Also, these agents can be thought of as being polypeptides, with a first and a second amino acid sequence region. The first region preferably includes a first domain and a second domain. Preferably, the first domain of the first amino acid sequence comprises a targeting moiety. In one embodiment, the targeting moiety is able to bind to surface receptors of the spinal cord neurons under physiological conditions. More preferably, the targeting moiety specifically binds a receptor on a spinal cord dorsal horn neuron, for example a projection neuron.
Preferably, the second domain comprises a heavy chain or a portion thereof of a clostridial neurotoxin. Even more preferably, the HN of the heavy chain is able to facilitate the transfer of the polypeptide across an endosome membrane into the cytosol of the neuron. In one embodiment, the second domain of the first amino acid sequence comprises a clostridial neurotoxin heavy chain. More preferably, the clostridial neurotoxin heavy chain is derived from Clostridium botulinum neurotoxin type A. Even more preferably, the heavy chain is derived from the HN of Clostridium botulinum neurotoxin type A. In yet another embodiment, the heavy chain may be derived from Clostridial botulinum types B, C, D, E, F, G and mixtures thereof. Also, the heavy chain may be derived from Clostridial baratii and Clostridial butyricum. Additionally, the heavy chain, preferably the HN, may be derived from Clostridial tetani. 
The second amino acid sequence region preferably comprises the L chain. The L chain is the effective therapeutic element having biological activity because, as discussed above, once it is transferred inside the neuron it interferes with the exocytosis process of neurotransmitter. Preferably, the light chain is derived from Clostridial botulinum neurotoxin type A. According to another broad aspect of this invention recombinant techniques are used to produce the clostridial neurotoxin components of the agents. The technique includes steps of obtaining genetic materials from either DNA cloned from natural sources, or synthetic oligonucleotide sequences, which have codes for clostridial neurotoxin components including clostridial neurotoxins, modified clostridial neurotoxins and fragments thereof. The genetic constructs are incorporated into host cells for amplification by first fusing the genetic constructs with a cloning vectors, such as phages or plasmids. Then the cloning vectors are inserted into hosts, preferably E. coli""s. Following the expressions of the recombinant genes in host cells, the resultant proteins can be isolated using conventional techniques. The clostridial neurotoxin components derived from the recombinant techniques can then be chemically coupled to targeting moieties. Preferably, the linkages between the clostridial components and the targeting moieties include an appropriate spacer regions.
In another embodiment, the genetic constructs include genes coding for both the clostridial neurotoxin components and the targeting moieties, for example, forming fusion proteins. Additionally, the genetic constructs may include genes coding for appropriate spacer regions between the clostridial neurotoxin components and the targeting moieties. From this aspect, the agents may be thought of as polypeptides comprising a first amino acid sequence region and a second amino acid sequence region. The first region may further comprise a first domain and a second domain. The details of these regions and domains are described above.
In another embodiment, the required L-HN, which may be a hybrid of an L chain and an HN from different clostridial toxin types, is expressed recombinantly as a fusion protein. Such LHN hybrid may also be coupled to the targeting moiety, which may further include one or more spacer regions between them.
In another embodiment of the invention the L chain of a clostridial neurotoxin, or a fragment of the L chain containing the endopeptidase activity, is expressed recombinantly as a fusion protein with the HN of the H chain and the targeting moiety which can also affect the internalization of the L chain, or fragment thereof containing the endopeptidase activity, into the cytoplasm of the cell. The expressed fusion protein may also include one or more spacer regions.
There are many advantages to producing these agents recombinantly. For example, production of neurotoxin from anaerobic Clostridium cultures is a cumbersome and time-consuming process including a multi-step purification protocol involving several protein precipitation steps and either prolonged and repeated crystallization of the toxin or several stages of column chromatography. Significantly, the high toxicity of the product dictates that the procedure must be performed under strict containment (BL-3). During the fermentation process, the folded single-chain neurotoxins are activated by endogenous clostridial proteases through a process termed nicking. This involves the removal of approximately 10 amino acid residues from the single-chain to create the dichain form in which the two chains remain covalently linked through the intrachain disulfide bond.
The nicked neurotoxin is much more active than the unnicked form. The amount and precise location of nicking varies with the serotypes of the bacteria producing the toxin. The differences in single-chain neurotoxin activation and, hence, the yield of nicked toxin, are due to variations in the type and amounts of proteolytic activity produced by a given strain. For example, greater than 99% of Clostridial botulinum type A single-chain neurotoxin is activated by the Hall A Clostridial botulinum strain, whereas type B and E strains produce toxins with lower amounts of activation (0 to 75% depending upon the fermentation time). Thus, the high toxicity of the mature neurotoxin plays a major part in the commercial manufacture of neurotoxins as therapeutic agents.
The degree of activation of engineered clostridial toxins is, therefore, an important consideration for manufacture of these materials. It would be a major advantage if neurotoxins such as botulinum toxin and tetanus toxin could be expressed, recombinantly, in high yield in rapidly-growing bacteria (such as heterologous E. coli cells) as relatively non-toxic single-chains (or single chains having reduced toxic activity) which are safe, easy to isolate and simple to convert to the fully-active form.
With safety being a prime concern, previous work has concentrated on the expression in E. coli and purification of individual H and L chains of tetanus and botulinum toxins; these isolated chains are, by themselves, non-toxic; see Li et al., Biochemistry 33:7014-7020 (1994); Zhou et al., Biochemistry 34:15175-15181 (1995), hereby incorporated by reference herein. Following the separate production of these peptide chains and under strictly controlled conditions the H and L subunits can be combined by oxidative disulphide linkage to form the neuroparalytic di-chains.
In another broad aspect of this invention, methods are provided for the treatment of pain which comprise administering effective doses of the agents according to the invention. The agents described in this invention can be used in vivo, either directly formulated or as a pharmaceutically acceptable salt, for treatment of pain.
For example, in a preferable embodiment, agents according to the invention can be administered by spinal injection (epidural or intrathecal) at the level of the spinal segment involved in the innervation of an affected organ for the treatment of pain. This is, for example, applicable in the treatment of deep tissue pain, such as chronic malignant pain.
As used herein xe2x80x9cintraspinalxe2x80x9d means into or within the epidural space, the intrathecal space, the white or gray matter of the spinal cord or affiliated structures such as the dorsal root and dorsal root ganglia.
In another aspect of the invention, there are provided methods for treatment of pain which comprise locally administering directly to a painful, benign bone tumor of a human patient therapeutically effective doses of an agent in accordance with the invention.
Examples of neoplasms which can be treated according to the present invention are benign bone tumors of cartilaginous origin such as enchondroma, osteochondroma, chondroblastoma and chondromyxoid, all of cartilaginous origin, as well as benign bone tumors of bone origin include osteoid osteoma and osteoblastoma. An agent, such as botulinum toxin-substance P can require according to the methods of the present invention, from about 1 to 7 days to achieve an antinociceptive effect, or to begin to achieve a necrotic effect upon a bone tumor. Thus, malignant bone tumors are excluded from the scope of the present invention because such tumors are preferably treated by a protocol with immediate effects such as surgical excision or radiotherapy, so as to prevent the tumor from metastasizing.
Additionally, an agent according to the present invention may be locally administered in vivo directly to the site of the tumor, whether on or within a bone. Known local drug administration methods suitable for this purpose include by long needle for bolus injection and by insertion of a controlled release implant.
In one embodiment of the invention, the agent of the invention reduces pain in the subject. For example, pain is reduced by at least 20%. In a more preferred embodiment, the pain in the subject is reduced by at least 50%. In an even more preferred embodiment, the pain is reduced by at least 80%.
Preferably, clostridial neurotoxin components of agents used to practice a method within the scope of the present invention comprise botulinum toxins, such as one of the type A, B, C, D, E, F or G. Preferably, the botulinum toxin used is botulinum toxin type A, because of its high potency in humans and ready availability. The targeting moiety of the agents used to practice the method herein is preferably a substance P.
An intraspinal route for administration of a neurotoxin according to the present disclosed invention can be selected based upon criteria such as the solubility characteristics of the agents chosen as well as the amount of the agents to be administered. The amount of the agents administered can vary widely according to the particular disorder being treated, its severity and other various patient variables including size, weight, age, and responsiveness to therapy. For example, the extent of the area of CNS afferent pain neuron somata influenced is believed to be proportional to the volume of agents injected, while the quantity of the analgesia is, for most dose ranges, believed to be proportional to the concentration of agents injected. Furthermore, the particular intraspinal location for agents administration can depend upon the dermosome location of the pain to be treated. Methods for determining the appropriate route of administration and dosage are generally determined on a case by case basis by the attending physician. Such determinations are routine to one of ordinary skill in the art (see for example, Harrison""s Principles of Internal Medicine (1998), edited by Anthony Fauci et al., 14th edition, published by McGraw Hill).
Preferably, the intraspinal administration is carried out intrathecally because of the greater ease in which the relatively larger intrathecal space is accessed and because the preferred agents generally exhibits low solubility in the lipid rich epidural environment. It is found that both inflammatory and neuropathic pain can be effectively treated by the disclosed methods without significant muscle spasticity or flaccidity or other side effects.
Intraspinal administration of the agents according to the present invention can be by various routes such as by catheterization or by spinal tap injection. The long lasting nature of the therapeutic effects of the present invention substantially removes the need for chronic antinociceptive drug administration, so that the present methods are advantageously practiced by infrequent spinal tap injection of the agents. Additionally, an intrathecal spinal tap agents administration route facilitates a more precise and localized delivery of agents with less danger of damage to the CNS, as compared to moving a catheter to access other CNS locations.
Intrathecal agents can be administered by bolus injection or by catheterization. The catheter can be inserted at L3-4 or at L4-5, a safe distance from the spinal cord which in humans terminates at L1, and guided upward in the subarachnoid space to rest at the desired site. For pain management, placement of the catheter or location of bolus injection by syringe depends on the site of the perceived pain, and the physicians preference. It is important to note that therapeutic agent administration according to the present disclosed methods can be carried out before the occurrence of, or during the experience of a nociceptive event or syndrome.
It is found that an agent, such as the LHN (derived from botulinum toxin type A)xe2x80x94substance P, can be intraspinally administered according to the present disclosed methods in amounts between about 1 U to about 500 U. Preferably the amounts are between about 10 U and about 300 U. More preferably the amount is between about 10 and about 200 U, such as about 70 U.
In a human patient, the therapeutically effective doses (when the clostridial neurotoxin component is derived from a botulinum toxin type A) can be amounts between about 10xe2x88x923 U/kg and about 35 U/kg. A dose of about 10xe2x88x923 U/kg can result in an antinociceptive effect if delivered directly to or onto the dorsal horn of the CNS and/or if agents delivery is assisted by methods such as iontophoresis. Intraspinal administration of less than about 10xe2x88x923 U/kg does not result in a significant or lasting therapeutic result. An intraspinal dose of more than 35 U/kg approaches a lethal dose of an agent such as the L-HN (derived from botulinum toxin type A)xe2x80x94substance P. It is desired that the agents used to obtain either antinociceptive effect contact the nerves of the CNS so as to favorably influence or down regulate the perception of pain in the innervated organ or tissue. Thus, intraspinal administration of agents by, for example, epidural injection can require an increase of the dosage by a factor of about ten to account for dilution of the agents upon diffusion from the epidural space to the intrathecal space and thence to the exterior nerves of the CNS.
A preferred range for intrathecal administration of an agent, such as the LHN(type A)xe2x80x94substance P, so as to achieve an antinociceptive effect in the patient treated is from about 10xe2x88x922 U/kg to about 10 U/kg. A more preferred range for intrathecal administration of an agent, such as the LHN (derived from botulinum toxin type A)xe2x80x94substance P, so as to achieve an antinociceptive effect in the patient treated is from about 10xe2x88x921 U/kg to about 10 U/kg. Less than about 10xe2x88x921 U/kg can result in the desired therapeutic effect being of less than the optimal or longest possible duration, while more than about 10 U/kg can still result in some symptoms of muscle flaccidity. A most preferred range for intrathecal administration of an agent, such as the L-HN(derived from botulinum toxin type A)xe2x80x94substance P, so as to achieve an antinociceptive effect in the patient treated is from about 1 U/kg to about 10 U/kg. Intrathecal administration of an agent, such as the L-HN(derived from botulinum toxin type A)xe2x80x94substance P, in this preferred range can provide dramatic therapeutic success. Furthermore, our experimental work indicates that a dose of about 3 U/kg can provide significant and long lasting antinociceptive effect without significant side effects for the treatment of inflammatory and neuropathic pain in human patients.
Although intraspinal administration of the agents is preferred for the treatment of pain, other routes of administration are possible. For example, the agent according to the invention can also be locally applied to a peripheral site of pain to alleviate such pain. A specific example of this is treatment by local application of the agents into a joint affected by inflammatory pain. Another example is treatment of muscular pain by subcutaneous, preferably intramuscular, injection of the agents into the location of pain.
The present invention includes within its scope the use of any agent which has a long duration antinociceptive effect when applied centrally or peripherally into a patient. For example, agents having the clostridial neurotoxin components made by any of the species of the toxin producing Clostridium bacteria, such as Clostridium botulinum, Clostridium butyricum, Clostridium beratti and Clostridium tetani can be used or adapted for use in the methods of the present invention. Additionally, all of the botulinum serotypes A, B, C, D, E, F and G can be advantageously used in the practice of the present invention, although type A is the most preferred and type B the least preferred, as explained above. Practice of the present invention can provide an analgesic effect, per injection, for 2 months or longer, for example 6 months, in humans.